Owing to the advancement of medical science, the survival rate of cancer patients is increasing. However, the rate of cancer development is also increasing according to the change of environmental factors and extended average life span. Up to date, many studies have been undergoing to treat cancer, and accordingly new drugs and treatment methods for cancer have been developed with improved treatment effect on cancer patients. However, in spite of the breakthrough in cancer treatment agents and methods such as surgery, radiotherapy and chemotherapy, the treatment effect on malignant tumor is still limited. Furthermore, side effects resulted from non-specific cytotocixity and relapse of cancer are still problems to be taken care of. To overcome the above problems, a new treatment method has been actively tried and under development, including immunotherapy. Immunotherapy has advantages of reducing side effects caused by systemic toxicity by inducing tumor-specific toxicity and improving the conventional cancer treatment method by establishing positive memory response against tumor antigen.
Anticancer cellular vaccine using antigen presenting cells can activate CD8+ T cells and CD4+ T cells effectively, resulting in excellent anticancer effect. The most frequently used cells for antigen presenting cell vaccine are dendritic cells, which uptake antigen and present thereof to effector cells along with costimulatory signal and therefore the dendritic cells can activate effector cells and induce strong immune responses. The cellular immunotherapeutic agent using dendritic cells is prepared and treated to a patient by the following steps; separating dendritic cells or monocytes, the precursors of the dendritic cells, from bone marrow or peripheral blood of a patient; proliferating and differentiating thereof; introducing an antigen; and administering the cells to the patient. The administered dendritic cells present specific antigen to T cells and thereby activate T cells to induce antigen-specific immune responses effectively. In spite of such advantages, the development of the cellular immunotherapeutic agent using dendritic cells is still limited because the number of dendritic cells which exist in peripheral blood and lymphoid tissues is small and isolation of the dendritic cells is difficult and ex-vivo culture might be required for several days when the cells are differentiated from monocytes. Therefore, it is required to develop an alternative improved cellular immunotherapeutic agent.
It is well understood that invariant natural killer T cells (iNKT cells) play a crucial role in a variety of immune responses and in immunopathology as a whole. Ligand-mediated activation of iNKT cells lead to the activation of T, B and NK cells as well as dendritic cells. Injection of alpha-galactosylceramide (αGalCer), an iNKT ligand, generates antitumor immunity via the activation of NK and T cells (Moodycliffe A M et al., Nat Immunol 1:521-525, 2000). The iNKT cells govern the response to self- and exogenous-antigens and determine whether autoimmune or immune response will be induced (Kronenberg M, Annu Rev Immunol 23:877-900, 2005; Park S H & Bendelac A, Nature 406:788-792, 2000).
Alpha-galactosylceramide (αGalCer) is a kind of glycolipid extracted from marine sponge, which is the ligand of natural killer T cell (NKT cell) having Vα14+ T cell receptor (TCR) and presented to NKT cells by CD1d molecule on antigen presenting cells (APC) (Kawano et al., Science 278:1626, 1997). The activation of the natural killer T cells by the natural killer T cell ligand leads to the mass-production of cytokine such as IFN-γ and IL-4, by which immune responses against either specific disease or infection can be controlled (Chen et al., J Immunol 159:2240, 1997; Wilson et al., Proc Natl Acad Sci USA 100:10913, 2003).
Unlike in healthy people, the number of immature myeloid cells (IMCs) increased in cancer patients which include immature macrophages, granulocytes, immature dendritic cells, monocytes and myeloid cells in early differential stage. Significantly increased level of IMCs was also detected in blood, bone marrow, spleen and tumor tissues of an animal model transplanted with tumor cells. Particularly in a mouse model, the expressions of CD11b and Gr-1 are observed on the surface of IMCs. The level of CD11b+/Gr-1+ cells in a healthy mouse blood and spleen is as low as up to 4%, which is because that CD11b+/Gr-1+ cells are the precursors of macrophages and dendritic cells, so that they can be differentiated into mature macrophages and dendritic cells if proper cytokine is provided. In cancer patients, however, CD11b+/Gr-1+ cells are not differentiated any more and accumulated because of tumor derived factors (IL-6, IL-10, VEGF, GM-CSF, etc). Since IMCs are accumulated at high level in blood of a cancer patient, it is easy to obtain a large amount of the cells. In addition, when monocytes are isolated to produce dendritic cell vaccine, it is difficult to gate out a large number of IMCs. IMCs, proliferated and accumulated in cancer patients and animals transplanted with tumor, are known to inhibit immune system. However, it is highly expected to improve immunogenicity by giving a proper stimulus.
Recently, it has been proved that the immunogenicity of dendritic cells has been enhanced by activating natural killer T cells (Kronenberg M et al., Annu Rev Immunol 23:877-900, 2005; Park S H et al., Nature 406:788-792, 2000). Based on that, the present inventors activated natural killer T cells by presenting natural killer T cell ligand to B cells for the first time, and further induced cytotoxic T cell responses against the antigen loaded on B cells by increasing immunogenicity of the B cells with the help of natural killer T cell, followed by confirmation that the effect was similar to that of dendritic cell vaccine (Chung Y et al., Cancer Res 66(13):6843-6850, 2006). However, there is no report saying that the improvement of immunogenicity by the activation of natural killer T cells might be exhibited not only in B cells but also in monocytes, the precursors of dendritic cells, or in immature myeloid cells (IMCs). Thus, in order to investigate whether monocytes and IMCs can be effectively used for the anticancer cellular vaccine, the present inventors loaded both antigen peptide and αGalCer to monocytes or IMCs, or loaded αGalCer to monocytes or IMCs which were transduced with adenovirus expressing an antigen, which was then administered into a subject. And further, the present inventors completed this invention by confirming thereby that immunization with monocytes- or IMCs-based vaccine induced the antigen specific immune responses and the significant anticancer effects.